The Microsoft founder is urging the UK to keep spending 0.7% of its national income on foreign aid, saying it is proof of its goodwill and humanity.

Theresa May has refused to say if she will retain the spending pledge in the Conservative’s election manifesto.

But the Scottish Tory leader pledged her own “absolute” commitment to it.

Ruth Davidson told BBC Newsnight: “I think that international aid not only benefits… the countries that receive it but we benefit too.

“I think we have a commitment to 0.7% on aid.

‘Moral courage’

“I think it takes moral courage to be one of the leading countries that espouses that, when there are a lot of countries that don’t do it.”

The current commitment equated to more than £12bn in 2015.

At a speech in London, Mr Gates said aid spending was not just altruistic, but helped the UK achieve its strategic goals, such as reducing global outbreaks of infectious diseases or avoiding war and large-scale migration.

There has been growing speculation that the Conservatives will attempt to row back on the aid commitment in their manifesto.

Newsnight political editor Nick Watt said there was pressure in Whitehall to subsume aid spending in a larger budget, which would include defence and trade.

This would allow the government more flexibility on how the cash was spent.

The commitment to spend 0.7% of national income – or GDP – on foreign aid was enshrined in law with the backing of the Tory-Liberal Democrat coalition in 2015.

Former International Development Secretary Andrew Mitchell told Newsnight: “It is a core promise of the Conservative Party and I very much hope it will be retained.

“Around the world we are lauded and respected for the lives we are saving as a result of this budget, but in Britain it receives very hostile treatment from elements of the press.”

Former No 10 policy chief Camilla Cavendish told the programme the aid commitment was “under threat” and she was concerned it was too high.

She said: “The UK is the second biggest aid donor in the world… many people do think it’s too much.”

‘Getting something back’

Mr Gates, who has done a round of interviews on the issue, told the Spectator: “In the case of the UK government, aid is under 2% of the budget… and applied in places where the interventions are at least a hundred times more effective than anything you’d do domestically.

“If you can’t save a life for less than 1,000 dollars, it’s not done.

“Nor is it done unless there’s a strategic goal – in terms of reducing pandemics, or creating stability to avoid war and migration.

“So you’re getting something back, avoiding problems for the UK and in particular the US.”

Brexit backdrop

Mr Gates also questioned whether the UK was stepping away from its international commitments amid the backdrop of Brexit.

“Are you just getting away from the rule-setting on migration and tariffs, or is it a statement about stepping away from the entire world, and being generous to others?” he said.

In the past, the prime minister has praised Britain’s aid spending as proof of its global leadership.

But in the Commons on Wednesday, Mrs May refused to confirm that her party’s election manifesto would renew the commitment.

A Conservative spokesman said the party would set out its plans in due course.